The long-term objective of this research is to explain the mechanism of insulin action at the molecular level. The specific objective of the proposed study is to test and substantiate the working hypothesis recently proposed from this laboratory as well as from Cushman's laboratory at NIH. According to the hypothesis, insulin stimulates glucose transport in fat cells by promoting translocation of the glucose transport activity to the plasma membrane from an intracellular storage site. In the proposed study, we will measure the glucose transport activity in a cell-free liposome system reconstituted with the glucose transport activities solubilized from the plasma membrane-rich fraction and Golgi-rich fraction. The translocation hypothesis predicts that insulin changes the two transport activities to the same extent towards opposite directions. However, the apparent effect of insulin currently observed in the Golgi-rich fraction is larger than that in the plasma membrane fraction. Therefore, we plan to investigate the reason for this paradoxical observation.